Our understanding of extensional tectonics have improved substantially within the last three decades based on geological, geophysical, geochemical studies, and analog and computer modeling in the regions extension have taken place. These regions include both sides of the Atlantic Ocean, Basins and Ranges of Western North America, and the Aegean Region of Eastern Europe and Western Asia. However, there are still many important questions.  These include determining a) evolution of extensional basins; b) the role of strike-slip faulting in extensional processes; c) amount and percentage of cumulative extension in regions experiencing continental extension; d) geometry of extensional features in the middle and lower crust; e) nature of upper mantle and asthenospheric flow, and f) seismic hazards. This symposium will bring together researchers working on important research questions of modern and ancient extensional tectonics and will provide a formal discussion to help the researchers to design research methods to test them.